Position sensing a location pin in a welding electrode

ABSTRACT

An apparatus having a housing, a location pin, a lever and a sensor is disclosed. The housing may be configured to receive a weld head. The location pin may be configured to move linearly in the housing in response to a force between the location pin and a part to be welded. The lever may be rotatably attached to the housing and configured to convert a linear position of the location pin relative to the housing into an angular position of a shaft relative to the housing. The sensor may be coupled to the shaft and configured to generate a value representative of the linear position of the location pin by a measurement of the angular position of the shaft.

FIELD OF THE INVENTION

The present invention relates to resistance welding generally and, more particularly, to a method and/or architecture for position sensing a location pin in a welding electrode.

BACKGROUND OF THE INVENTION

Detecting a proper orientation of a weld fastener before applying a welding current is an issue in conventional welding assemblies. A mis-orientated or incorrect weld fastener can cause destruction of the welding electrodes, destruction of the weld fastener and destruction of the weld tooling. Any such destruction causes delays in production and incurs an expense in replacing the destroyed parts. Welding with the wrong fastener, or welding with the correct fastener but in the wrong orientation, results in rejections of the welded fasteners, failures in the welded fasteners in service and rework to replace the mis-welded fasteners.

It would be desirable to implement position sensing a location pin in a welding electrode.

SUMMARY OF THE INVENTION

The present invention concerns an apparatus having a housing, a location pin, a lever and a sensor. The housing may be configured to receive a weld head. The location pin may be configured to move linearly in the housing in response to a force between the location pin and a part to be welded. The lever may be rotatably attached to the housing and configured to convert a linear position of the location pin relative to the housing into an angular position of a shaft relative to the housing. The sensor may be coupled to the shaft and configured to generate a value representative of the linear position of the location pin by a measurement of the angular position of the shaft.

The objects, features and advantages of the present invention include providing position sensing a location pin in a welding electrode that may (i) monitor an orientation of a weld part, (ii) monitor a presence/absence of the weld part, (iii) sense a position of a location pin in a way immune to electromagnetic fields generated during the welding process, (iv) incorporate inexpensive monitoring components, (v) replicate a height of conventional electrodes without the position sensing, (vi) incorporate a limit switch, (vii) incorporate a voltage detector, (viii) incorporate a visual indicator, (ix) incorporate an electrical angle sensor, (x) incorporate a mechanical angle sensor, (xi) incorporate an optical angle sensor, (xii) incorporate a pneumatic angle sensor, (xiii) provide ease of maintenance and/or (xiv) easily adapt to existing weld assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which:

FIG. 1 is a cross-sectional exposed view of an apparatus in accordance with a preferred embodiment of the present invention;

FIG. 2 is another cross-sectional view of the apparatus;

FIG. 3 is a cross-sectional view of another apparatus;

FIG. 4 is a diagram of an electro-mechanical angle sensor;

FIG. 5 is a cross-sectional view of an optical angle sensor;

FIG. 6 is a detailed diagram of the optical angle sensor;

FIG. 7 is a diagram of a pneumatic angle sensor;

FIG. 8 is a cross-sectional view of another apparatus;

FIG. 9 is a cross-sectional view of a load position;

FIG. 10 is a cross-sectional view before welding;

FIG. 11 is a cross-sectional view after the welding; and

FIG. 12 is a cross-sectional view with an upside down fastener.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the present invention may provide one or more monitoring techniques of a position, an orientation and/or an absence of a part to be welded before welding begins. The monitoring techniques are generally immune to electromagnetic fields generated by a welding current applied by a welding electrode to the part to be welded. A welding electrode incorporating the monitoring techniques may have a height matching or similar to that of existing welding electrodes without the monitoring techniques. Where incorporated into one of a pair of welding electrodes (e.g., a lower and/or stationary electrode), the welding electrodes may be easily adapted to existing welding machines and provide ease of maintenance.

A location pin of the welding electrode may move linearly in a housing to determine an orientation and/or absence of the part to be welded. A position of the location pin may be monitored (or sensed) by converting the position of the location pin into an angular position and measuring the angular position. The monitoring techniques may incorporate low-cost sensors. The sensors generally include, but are not limited to, a limit switch, a voltage detector, a visual indicator, an electrical angle sensor, a mechanical angle sensor, an optical angle sensor and/or a pneumatic angle sensor. Other sensors that measure a rotation of a shaft may be implemented to meet the criteria of a particular design application.

Referring to FIG. 1, a cross-sectional exposed view of an example implementation of an apparatus 100 is shown in accordance with a preferred embodiment of the present invention. The apparatus (or system) 100 may implement a welding electrode. The apparatus 100 may be configured to weld a fastener (or part) 90 to an object (or component) 92. The welding may be achieved by electrical resistance welding.

The apparatus 100 generally comprises a housing (or assembly) 102, a location pin (or assembly) 104, a cavity (or bore) 106, a port (or bore) 108, a spring (or assembly) 110, a rotary lever (or arm) 112, a shaft (or rod) 114, a weld head (or electrode) 116, a rotary indicator (see FIG. 2) 118 and an encoder (or monitor) 120. In operation, the fastener 90 and the object 92 are brought into contact with the weld head 116 at an end of the housing 102. The location pin 104 is generally received in an opening of the fastener 90 and an opening of the object 92. A linear distance that the location pin 104 travels into the opening of the fastener 90 generally indicates if the fastener 90 is selectively (or alternatively) in a proper orientation, an improper orientation (e.g., upside down), missing and/or is an incorrect part.

The location pin 104 may be pushed (or biased) toward the fastener 90 by air pressure created in the cavity 106 through the port 108 and/or by the spring 110. As the assembly 100 and the fastener 90/object 92 are brought together, the location pin 104 generally contacts the fastener 90. A force created between the fastener 90 and the location pin 104 may cause the location pin 104 to move into the housing 102 and compress the spring 110. The movement may stop when the weld head 116 contacts the object 92. The weld head 116 generally conveys the welding current to the object 92.

The rotary lever 112 is generally disposed between the location pin 104 and the spring 110. The linear motion of the location pin 104 may be converted (or translated) into an angular motion of the rotary lever 112 about the shaft 114. A center of rotation of the shaft 114 is generally offset from a centerline of the location pin 104 (e.g., offset to the left in the figure). The sensor 120 may measure an angle (e.g., an absolute angle or a relative angle) of the shaft 114 in reference to the housing 102. An angle value of the measured angle of the shaft is generally proportional to a distance (e.g., Z) traveled by the location pin 104 in reference to the housing 102 while the fastener 90/the object 92 are moved from an initially-contacting (or load) position to a welding position. The distance (or position) Z that the location pin 104 travels may be used to determine if the welding process may be allowed (e.g., a proper fastener 90 in a proper orientation) or should be denied (e.g., wrong fastener, missing fastener, incorrect orientation, and/or any other error).

Referring to FIG. 2, another cross-sectional view of the apparatus 100 is shown. A combination of the rotary indicator 118 and the encoder 120 may form a sensor (or detector) 122. The sensor 122 may be in communication with a circuit 124 via one or more electrical signals.

The rotary indicator 118 may be coupled to the shaft 114. In various embodiments, the coupling may be a direct connection or an indirect connection between the rotary indicator 118 and the shaft 114. The coupling generally causes the rotation of the shaft 114 to be conveyed to the rotary indicator 118. The angular position of the rotary indicator 118 relative to the housing 102 may be identical to the angular position of the shaft 114. The encoder 120 may be mounted on the housing 102 in alignment with the rotary indicator 118.

In some embodiments, the rotary indicator 118 may be implemented as a positioning element. For example, the rotary indicator 118 may be a positioning element (e.g., part number P1-Ri-SR14, available from Turck Inc., Minneapolis, Minn.) for inductive angle sensors. In some embodiments, the encoder 120 may be implemented as an inductive angle sensor (e.g., part number Ri30-P2-QR14, available from Truck Inc.) In various embodiments, the rotary indicator 118 and the encoder 120 may be arranged in a non-contact configuration.

The sensor 122 generally provides an oscillator circuit coupling between a transducer in the encoder 120 and a sensor in the rotary indicator 118. The oscillator circuit coupling may be immune to electromagnetic interference, such as the electromagnetic fields generated during the welding process. The sensor 122 may generate an analog electrical signal proportional to an angle of the rotary indicator 118 relative to the encoder 120. The analog electrical signal may be digitized in the circuit 124 to a finite resolution (e.g., 12 bits). At 12-bits resolution, the circuit 124 may monitor an angle value of the shaft 114 to a few hundredths of a degree (e.g., ≦0.09 degrees). Additional details of the sensor 122 may be found in datasheet “Inductive Angle Sensor With Analog Output”, Ri30P2-QR14-LiU5X2-0,3-RS4, by Turck Inc., which is hereby incorporated by reference in its entirety. Other types of electrical angle sensors may be implemented to meet the criteria of a particular design application.

The circuit 124 may implement a detector circuit. The circuit 124 is generally operational to measure the electrical signal generated by the sensor 122. Based on the measurement, the circuit 124 may provide status of the location pin 104 position to a weld control circuit (not shown). The weld control circuit generally controls the welding current applied to the weld head 116. The status may include, but is not limited to, a proper orientation of the fastener 90, an incorrect orientation of the fastener 90, the fastener 90 is missing and/or an incorrect fastener is detected. For example, the angular position measured by the sensor 122 may be translated in the circuit 124 to a linear position of the location pin 104. Where the location pin 104 is in a “correct orientation” position range, the circuit 124 may signal the weld control circuit that the fastener 90/object 92 are ready to weld. Where the location pin 104 is in an “incorrect orientation” position range, the circuit 124 may signal the weld control circuit that the fastener 90 is present and in the wrong orientation. Where the location pin 104 is in one or more possible “wrong part” position ranges, the circuit 124 may signal the weld control circuit that an incorrect fastener is loaded. Where the location pin 104 is in a “missing” position range, the circuit 124 may signal the weld control circuit that the fastener 90 and/or object 92 is missing. Other position ranges of the location pin 104 may be implemented to meet the design criteria of a particular application.

Referring to FIG. 3, a cross-sectional view of an example implementation of an apparatus 100 a is shown. The apparatus 100 a may be a variation of the apparatus 100. The apparatus 100 a generally includes the housing 102, a spring (or assembly) 110 a, a shaft (or rod) 114 a and a sensor (or detector) 122 a. The sensor 122 a may be in electrical communication with a circuit 124 a. The spring 110 a (e.g., a rotary spring) may be a variation of the spring 110. The shaft 114 a may be a variation of the shaft 114. The sensor 122 a may be a variation of the sensor 122. The circuit 124 a may be a variation of the circuit 124. Other elements of the apparatus 100 may be included in the apparatus 100 a.

The sensor 122 a may implement an electrical angle sensor. The sensor 122 a may be operational to convert the angular position of the shaft 114 a into an angle value. The angle value may be presented in one or more electrical signals to the circuit 124 a. The shaft 114 a may be longer than the shaft 114. The shaft 114 a may extend outside the housing 102 and into the sensor 122 a. The circuit 124 a may be operational to measure the angle value measured by the sensor 122 a. The circuit 124 a may be operational to provide the status indications to the weld control circuit based on the measured angle value, similar to the circuit 124.

Referring to FIG. 4, a diagram of an example implementation of an electro-mechanical angle sensor 122 b is shown. The sensor 122 b may be a variation of the sensors 122 and/or 122 a. The sensor 122 b may be mounted to the housing 102. The sensor 122 b may be in electrical communication with a circuit 124 b. The circuit 124 b may be a variation of the circuits 124 and/or 124 a.

The sensor 122 b generally comprises a wheel (or disk) 130, an arm (or lever) 132, a detent 134 in the wheel 130, a contact switch (or relay) 136 and a latch (or limit switch) 138. The wheel 130 may be coupled, indirectly connected, or directly connected to the shaft 114 a. The circuit 124 b may be operational to provide the status indications to the weld control circuit based on the measured angle value, similar to the circuit 124.

As the location pin 104 is pushed into the housing 102, the wheel 130 may be turned by the shaft 114 a. In some embodiments, the arm 132 may be designed to press the contact switch 136 if the distance traveled by the location pin 104 indicates a present and properly oriented fastener 90. The circuit 124 b may electrically sense a change in the contact switch 136 from unpressed to pressed. While the contact switch 136 is pressed, the circuit 124 b may communicate to the weld control circuit that the fastener 90, the object 92 and the weld head 116 combination are in a correct orientation to be welded. While the contact switch 136 is unpressed, the circuit 124 b may communicate to the weld control circuit that at least one of the fastener 90, the object 92 and/or the weld head 116 combination is not ready for the weld process to take place.

A length from the center of rotation of the shaft 114 a to an outer end of the arm 132 may be greater than a length of the lever 112 (FIG. 1). The longer length of the arm 132 may provide a mechanical amplification of the distance Z that the location pin 104 is moved. A small movement of the location pin 104 may be translated into a larger linear movement of the contact switch 136 allowing for a more precise sensing of where the location pin 104 is positioned.

In other embodiments, the detent 134 and the latch 138 may be designed such that the detent 134 and the latch 138 are aligned with each other when the fastener 90, the object 92 and the weld head 116 combination are in a correct orientation to be welded. The circuit 124 b may be configured to electrically monitor the latch 138 to detect an aligned condition and a not align condition between the detent 134 and the latch 138. When aligned, the circuit 124 b may communicate to the weld control circuit that the welding process may take place. The circuit 124 b may be configured to treat a non-aligned condition between the detent 134 and the latch 138 as an indication that at least one of the fastener 90, the object 92 and/or the weld head 116 combination is not ready for the weld process to take place.

Referring to FIG. 5, a cross-sectional view of an example implementation of an optical angle sensor 122 c is shown. The sensor 122 c may be a variation of the sensors 122, 122 a and/or 122 b. The sensor 122 c may be mounted to the housing 102. The sensor 122 c may be in electrical communication with a circuit 124 c. The circuit 124 c may be a variation of the circuits 124, 124 a and/or 124 b.

The sensor 122 c may be directly or indirectly coupled or connected to the shaft 114 a. An electrical signal generated by the sensor 122 c may be proportional to an angle (absolute or relative) of the shaft 114 a. The electrical signal generated by the sensor 122 c may be received by the circuit 124 c. The circuit 124 c may examine the signal to determine if the fastener 90, the object 92 and the weld head 116 are properly aligned for the welding process to begin. Based on the angle value received in the electrical signal, the circuit 124 c may determine that one or more of the fastener 90, the object 92 and/or the weld head 116 are not ready for welding. The circuit 124 c may report the ready/not ready/missing part/wrong part determination to the weld control circuit. The circuit 124 c may be operational to provide the status indications to the weld control circuit based on the measured angle value, similar to the circuit 124.

Referring to FIG. 6, a detailed diagram of an example implementation of the sensor 122 c is shown. The sensor 122 c generally comprises an extension (or wheel) 140, a shutter (or block) 142, a light source 144 that shines a light beam 146 toward a light sensor 150. The shutter 142 may be aligned along an outer edge of the extension 140 to prevent the light beam 146 from reaching the light sensor 150 at some angles (as shown). The shutter 142 may permit the light beam 146 to reach the light sensor 150 along a path 148 at other angles. The extension 140 may be coupled (or indirectly connected or directly connected) to the shaft 114 a.

The circuit 124 c may receive an electrical signal from the light sensor 150. The electrical signal may indicate that the light bean 146 has either reached the sensor 150 or is blocked by the shutter 142. Before the location pin 104 engages the fastener 90, the light beam 146 may reach the light sensor 150. The circuit 124 c may monitor the light sensor 150 and communicate to the weld control circuit that the welding process should be inhibited. Where the location pin 104, the fastener 90 and the object 92 are present and properly aligned, the extension 140 may rotate the shutter 142 into the light beam 146 (as shown) to prevent the light beam 146 from reaching the light sensor 150. The circuit 124 c may sense the change in the electrical signal generated by the now-dark light sensor 150 and communicate to the weld control circuit that the welding process may proceed. If the location pin 104 travels too far, the light beam 146 may become unblocked by the shutter 142. The light sensor 150 may convey the illumination to the circuit 124 c. The circuit 124 c may communicate to the weld control circuit that something is wrong with the faster 90, the object 92 and/or the location pin 104. The weld control circuit may inhibit the welding process in such situations. In various embodiments, the shutter 142 may be configured such that the light bean 146 reaches the light sensor 150 only when the faster 90, the object 92 and the location pin 104 are properly positioned for welding, and block the light beam 146 otherwise.

A length from the center of rotation of the shaft 114 a to a point on the shutter 142 that engages the light beam 146 may be greater than a length of the lever 112 (FIG. 1). The longer length may provide a mechanical amplification of the distance Z that the location pin 104 is moved. A small movement of the location pin 104 may be translated into a larger angular movement of the shutter 142 allowing for a more precise sensing of where the location pin 104 is positioned.

The extension 140 may include markings 152. The markings 152 may provide a visual indication of the position of the location pin 104 relative to the housing 102. The visual indication may be used by an operator of the welding assembly to verify that the fastener 90, the object 92 and the weld head 116 are ready or not ready for the welding process to begin.

Referring to FIG. 7, a diagram of an example implementation of a pneumatic angle sensor 122 d is shown. The sensor 122 d may be a variation of the sensors 122, 122 a, 122 b and/or 122 c. The sensor 122 d may be mounted to the housing 102. The sensor 122 d may be in electrical communication with a circuit 124 d. The circuit 124 d may be a variation of the circuits 124, 124 a, 124 b and/or 124 c.

The sensor 122 d generally comprises a wheel (or disk) 160, a tube (or bore) 162 through the wheel 160, an input tube (or pipe) 164, an output tube (or pipe) 166 and a pressure sensor 168. An open end of the input tube 164 may receive a pressurized fluid or gas. The pressure sensor 168 may generate a pressure value proportional to a pressure in the output tube 166. The pressure value may be conveyed from the pressure sensor 168 to the circuit 124 d in an electrical signal. The circuit 124 d may be operational to provide the status indications to the weld control circuit based on the measured pressure value, similar to the circuit 124.

Before the location pin 104 engages the fastener 90, the tube 162 may block the pressure in the input tube 164 from reaching the pressure senor 168 via the output tube 166. The circuit 124 d may monitor the pressure sensor 168 and communicate to the weld control circuit that the welding process should be inhibited. Where the location pin 104, the fastener 90 and the object 92 are present and properly aligned, the wheel 160 may rotate the tube 162 into alignment with the input tube 164 and the output tube 166. The rotation effectively opens a valve formed by the wheel 160 and the tubes 162, 164 and 166. The circuit 124 d may sense the change in the pressure value in the electrical signal generated by the pressure sensor 168 and communicate to the weld control circuit that the welding process may proceed. If the location pin 104 travels too far, the tube 162 may rotate out of alignment with the tubes 164 and 166. The pressure sensor 168 may convey the reduced pressure to the circuit 124 d. The circuit 124 d may communicate to the weld control circuit that something is wrong with the faster 90, the object 92 and/or the location pin 104. The weld control circuit may inhibit the welding process in such situations.

Referring to FIG. 8, a cross-sectional view of an example implementation of an apparatus 100 b is shown. The apparatus 100 b may be a variation of the apparatus 100 and/or the apparatus 100 a. The apparatus 100 b may be used to weld a weld stud (or part) 90 a to the object 92. To account for different geometries between the weld stud 90 a and the fastener 90, the apparatus 100 b may include a push pin 104 a in place of the location pin 104. Operation of the apparatus 100 b may be similar to that of the apparatus 100 and/or the apparatus 100 a. Other elements of the apparatus 100 and/or the apparatus 100 a may be included in the apparatus 100 b.

Referring to FIG. 9, a cross-sectional view of the fastener 90 in a load position is shown. In the load position, the location pin 104 may be pushed (or biased) to a maximum distance out of the housing 102. The fastener 90, if present, may be in contact with the location pin 104 but does not apply any force to the location pin 104. If the fastener 90 is missing, the location pin 104 may also be pushed (or biased) to the maximum distance out of the housing 102. In the load position, the sensor 122 (or 122 a, 122 b, 122 c or 122 d) may be monitored by the respective circuit 124 (or 124 a, 124 b, 124 c or 124 d). The circuit 124 may report to the weld control circuit that the welding process should be inhibited.

Referring to FIG. 10, a cross-sectional view before welding is shown. The fastener 90 may be in contact with the object 92. The location pin 104 may be moved a predetermined (or anticipated) distance into the housing 102. In the before welding position, the sensor 122 (or 122 a, 122 b, 122 c or 122 d) may be monitored by the respective circuit 124 (or 124 a, 124 b, 124 c or 124 d). The circuit 124 may report to the weld control circuit that the welding process may begin.

Referring to FIG. 11, a cross-sectional view after the welding is shown. The fastener 90 may move slightly closer to the object 92 as protrusions on a bottom of the fastener 90 melt and weld the fastener 90 to the object 92. The location pin 104 may move the slight distance further into the housing 102. In the after welding position, the sensor 122 (or 122 a, 122 b, 122 c or 122 d) may be monitored by the respective circuit 124 (or 124 a, 124 b, 124 c or 124 d). The circuit 124 may report to the weld control circuit that the welding process was successful.

Referring to FIG. 12, a cross-sectional view with an upside down fastener 90 is shown. Where the fastener 90 is turned upside down relative to the object 92, the location pin 104 may be moved an improper distance into the housing 102. The improper distance may be different from the predetermined distance due to a geometry difference on opposing sides of the fastener 90. For example, a top side of the fastener 90 (e.g., the side normally facing away from the object 92), may include a beveled inside edge 94 (also see FIG. 11). If the fastener 90 is upside down, the beveled inside edge 94 may allow the location pin 104 to protrude a further distance out of the housing 102 than would normally be expected. The circuit 124 may monitor the further distance and communicate to the weld control circuit to inhibit the welding process because the fastener 90 is mis-oriented.

The functions and structures illustrated in the diagrams of FIGS. 1-12 may be designed, modeled and simulated using one or more of a conventional general purpose processor, digital computer, microprocessor, microcontroller and/or similar computational machines, programmed according to the teachings of the present specification, as will be apparent to those skilled in the relevant art(s). Appropriate software, firmware, coding, routines, instructions, opcodes, microcode, and/or program modules may readily be prepared by skilled programmers based on the teachings of the present disclosure, as will also be apparent to those skilled in the relevant art(s). The software is generally embodied in a medium or several media, for example a non-transitory storage media, and may be executed by one or more of the processors.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention. 

The invention claimed is:
 1. An apparatus comprising: a housing configured to receive a weld head; a location pin configured to move linearly in said housing in response to a force between said location pin and a part to be welded; a lever rotatably attached to said housing and configured to convert a linear position of said location pin relative to said housing into an angular position of a shaft relative to said housing; and a sensor coupled to said shaft and configured to generate a value representative of said linear position of said location pin by a measurement of said angular position of said shaft.
 2. The apparatus according to claim 1, wherein (i) said sensor is further configured to generate an electrical signal that conveys said value and (ii) said value indicates that said part to be welded is selectively one of (a) in a proper orientation, (b) in an improper orientation and (c) missing.
 3. The apparatus according to claim 1, wherein said sensor comprises (i) an indicator coupled to said shaft and (ii) an encoder configured to sense said angular position of said indicator relative to said housing to determine said value, and said encoder does not physically contact said indicator.
 4. The apparatus according to claim 1, wherein said sensor is an electrical angle sensor configured to generate an electrical signal that conveys said value based on said angular position of said shaft.
 5. The apparatus according to claim 1, wherein said sensor comprises (i) an arm coupled to said shaft and configured to convert said angular position of said shaft into a position at an end of said arm, said arm is longer than said lever and said end of said arm is opposite said shaft, and (ii) a switch configured to generate an electrical signal that conveys said value based on said position of said end of said arm.
 6. The apparatus according to claim 1, wherein said sensor comprises (i) an extension coupled to said shaft and configured to convert said angular position of said shaft into a position at an end of said extension, said end of said extension is remote from said shaft and includes a shutter that selectively passes and blocks a light and (ii) an optical sensor configured to generate an electrical signal that conveys said value based on said light.
 7. The apparatus according to claim 1, wherein said sensor is a pneumatic angle sensor configured to generate an electrical signal that conveys said value based on said angular position of said shaft.
 8. The apparatus according to claim 1, wherein said measurement of said angular position of said shaft is immune to a electromagnetic field generated by said weld head.
 9. The apparatus according to claim 1, wherein said apparatus is part of a welding electrode.
 10. A method for position sensing a location pin in a welding electrode, comprising the steps of: (A) moving said location pin linearly in a housing in response to a force between said location pin and a part to be welded, wherein said housing is configured to receive a weld head; (B) converting a linear position of said location pin relative to said housing into an angular position of a shaft relative to said housing using a lever; and (C) generating a value representative of said linear position of said location pin by a measurement of said angular position of said shaft.
 11. The method according to claim 10, further comprising the step of: generating an electrical signal that conveys said value, wherein said value indicates that said part to be welded is selectively one of (a) in a proper orientation, (b) in an improper orientation and (c) missing.
 12. The method according to claim 10, wherein said measurement comprises: coupling said angular position of said shaft to an indicator; and sensing said angular position of said indicator relative to said housing to determine said value with an encoder, wherein said encoder does not physically contact said indicator.
 13. The method according to claim 10, wherein said measurement is an electrical angle measurement configured to generate an electrical signal that conveys said value based on said angular position of said shaft.
 14. The method according to claim 10, wherein said measurement comprises: converting said angular position of said shaft into a position at an end of an arm coupled to said shaft, wherein said arm is longer than said lever and said end of said arm is opposite said shaft; and generating an electrical signal that conveys said value based on said position of said end of said arm.
 15. The method according to claim 10, wherein said measurement comprises: converting said angular position of said shaft into a position at an end of an extension coupled to said shaft, wherein said end of said extension is remote from said shaft and includes a shutter that selectively passes and blocks a light; and generating an electrical signal using an optical sensor that conveys said value based on said light.
 16. The method according to claim 10, wherein said measurement is a pneumatic angle measurement configured to generate an electrical signal based on said angular position of said shaft.
 17. The method according to claim 10, wherein said measurement of said angular position of said shaft is immune to a electromagnetic field generated by said weld head.
 18. An apparatus comprising: means for housing configured to receive a weld head; means for moving a location pin linearly in said means for housing in response to a force between said location pin and a part to be welded; means for converting a linear position of said location pin relative to said means for housing into an angular position of a shaft relative to said means for housing; and means for generating a value representative of said linear position of said location pin by a measurement of said angular position of said shaft. 